1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electro-optic device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
Attention has been directed to a technique for forming a transistor (also referred to as a thin film transistor (TFT)) using a semiconductor thin film formed over a substrate having an insulating surface. Such a transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). As a semiconductor thin film applicable to the transistor, a silicon based semiconductor material is widely known. Moreover, an oxide semiconductor has been attracting attention as another material.
For example, a transistor whose active layer includes an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) and having an electron carrier concentration of less than 1018/cm3 is disclosed (see Patent Document 1).